In some fields of use of catheters or similar devices, for example electrode lines, a pressure on adjacent tissue is relevant to the function of said catheter or similar device, and therefore detection of this contact force is of interest. This is particularly true for what are known as ablation catheters, with which areas of tissue are ablated or tissue parts are removed.
An ablation catheter (e.g., “TactiCath” by Endosense) is known, which makes it possible to measure the magnitude and direction of a force, that is to say the aforementioned contact force in the case of application, acting on the distal catheter end during an ablation process. This catheter utilizes the principle of what is known as an FBG (Fiber Bragg Grating) sensor, wherein three fibers each with an FBG sensor at the end of the fiber form the group of sensors required for a 3D force measurement; it being possible to incorporate said sensors at a signal processing unit for joint measurement signal processing. The sensors are applied externally to a deformable cylinder at an angular distance of 120°.
In U.S. Publication No. 2008/0285909, the operating principle of FBG sensors for determination of torsions or curvatures of the catheter body is described in detail, and the operating principle of the aforementioned force sensor with a plurality of FBG fibers on a deformable cylinder is also explained in this document.
As described in International Publication No. WO 2009/138957, a temperature compensation is provided by means of three electric thermocouples, because even small temperature changes or deviations between the individual sensors can cause significant measurement uncertainties with the FBG measurement method and, with an electrothermal ablation process, rather considerable temperature fluctuations can occur at the tip of the ablation catheter.
The optical measurement principle of FBG sensor systems is known in general and, in particular, in its use for force measurements and temperature measurements; for example see “www.wikipedia.org/wiki/Fiber_Bragg_grating” or A. Othonos, K. Kalli: “Fiber Bragg Gratings: Fundamentels and Applications in Telecommunications and Sensing” Artec House 1999, and (specifically based on voltage and temperature measurements) U.S. Pat. No. 5,399,854. A detailed explanation of the measurement principle is understood by one of ordinary skill in the art and, therefore, is not necessary herein.
Irrespective of this measurement principle, other solutions for a contact force measurement on a guide wire or catheter are also known, for example with use of an optical sensor, as described in International Publication No. WO 2009/007857, or with use of a semiconductor sensor at the tip of a guide wire, as described in International Publication No. WO 2008/003307. A more recent solution is disclosed in U.S. Publication No. 2012/0220879, which also is owned by the present Applicant.
The present invention is directed toward overcoming one or more of the above-identified problems.
In view of the above-mentioned prior art, an object lies in specifying a force sensor that is suitable for simple applications and has particularly simple signal processing. A further object lies in specifying a force measurement device that is likewise simplified in terms of its signal processing and that is suitable for multi-axis force or pressure detection and corresponding applications. A further object lies in specifying a catheter that is of simple design and, therefore, can be produced cost effectively for specific applications, wherein patient safety is ensured to a high degree with use of said catheter.